I did, ''Couldn’t refresh data adapter" came from my log file.
2018-06-05T12:01:41.489+02:00 ERROR [LookupDataAdapter] Couldn't refresh data adapter <switches_lookup_cache/5b11622368cb5c7ed8af88f4/@7793c60d>
java.lang.NullPointerException: null
at org.graylog2.lookup.adapters.CSVFileDataAdapter.doRefresh(CSVFileDataAdapter.java:102) ~[graylog.jar:?]
at org.graylog2.plugin.lookup.LookupDataAdapter.refresh(LookupDataAdapter.java:89) ~[graylog.jar:?]
at org.graylog2.lookup.LookupDataAdapterRefreshService.lambda$schedule$0(LookupDataAdapterRefreshService.java:142) ~[graylog.jar:?]
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511) [?:1.8.0_161]
at java.util.concurrent.FutureTask.runAndReset(FutureTask.java:308) [?:1.8.0_161]
at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$301(ScheduledThreadPoolExecutor.java:180) [?:1.8.0_161]
at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:294) [?:1.8.0_161]
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149) [?:1.8.0_161]
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624) [?:1.8.0_161]
at java.lang.Thread.run(Thread.java:748) [?:1.8.0_161]